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The targeted concentration of acoustic waves has significant implications for industrial nondestructive testing, ultrasound diagnosis, and medical treatment. Most conventional sound-focusing metasurfaces suffer from an untunable focus, narrow bandwidth, and fixed geometric configurations, which severely constrain their practical utility. In this paper, we propose a reconfigurable acoustic coding metasurface composed of two coding units with high transmittance and transmitted phases of 0 and π for realizing tunable and broadband sound focusing. Through the straightforward manipulation of each unit structure and alterations in the coding sequences, precise control of the focus position across the entire working plane is attainable, enabling both tunable axial-axis and off-axis sound-focusing effects. Moreover, the sound-focusing performance of the proposed metasurface is excellent within a broad frequency range from 3000 to 5500 Hz. The experimental results are consistent with theoretical expectations and numerical simulations. This work lays a practical foundation for the design of acoustic devices for tunable and broadband sound focusing. [ABSTRACT FROM AUTHOR]

The mode manipulation of Lamb waves plays an important role in damage detection and identification of damage types, location, and size. In this paper, we propose a composite phononic crystal (PC) plate with antisymmetric and symmetric PCs for realizing mode conversion from A0 to S0 mode of Lamb waves. The theoretical analysis, numerical simulations, and experimental validation are introduced and the mode conversion mechanism of the composite PC plate is systematically investigated. The effect of geometrical parameters on band structures of antisymmetric and symmetric PCs is first discussed. Then multi-physics field simulation models are developed and in-plane displacement fields are obtained in numerical simulations, which shows that the mode conversion is enhanced when the period number of the antisymmetric PC decreases and that of symmetric the PC increases. The composite PC plate specimens are fabricated with precision wire cutting technology for experimental measurements and the self-designed polyvinylidene fluoride (PVDF) comb transducer is used to stimulate the Lamb waves. The experimental results are consistent with the numerical simulations, which demonstrate that the proposed composite PC plate can achieve the mode conversion from A0 to S0 mode of Lamb waves. Our proposed structures have applicable values for the mode manipulation of Lamb waves in damage detection. [ABSTRACT FROM AUTHOR]

The late Na+ current has emerged as a therapeutic target for conditions characterized by depressed diastolic function, but whether enhanced Na+ fluxes in cardiomyocytes interfere with cellular and myocardial relaxation remain to be clarified. For this purpose, we employed mice with inducible, cardiac restricted deletion of the non-pore forming beta1 subunit of the Na+ channel (Scn1b -KO), a rodent model associated with enhanced Na+ influx in cardiomyocytes. Two-dimensional and Doppler echocardiography and ECGs were employed to evaluate cardiac function in Scn1b -KO and control (Ctrl) animals. Properties of Ca2+ transient and contractility were established in isolated left ventricular (LV) myocytes obtained by enzymatic digestion. Deletion of the Scn1b gene had no consequences on ejection fraction, whereas LV filling pattern was altered, isovolumic relaxation time prolonged (+30%), and electrical recovery, measured by the QT interval, was protracted (+14%). In a subgroup of animals, acute administration of GS967 (0.5 mg/kg body weight), a specific inhibitor of the late Na+ current, partly ameliorated diastolic indices and shortened the QT interval. At the cellular level, kinetics of cell shortening and Ca2+ transients were delayed in Scn1b -KO myocytes (n=609-693), with respect to Ctrl cells (369-298). Specifically, time to peak Ca2+ and time to 50% decay of the Ca2+ transient were increased in Scn1b -KO cells by 5% and 17%, respectively. Similarly, time to peak contraction and time to 50% relaxation were enhanced by 6% and 7% in Scn1b -KO. Interestingly, GS967 (300 nM) accelerated temporal parameters of contraction in Scn1b -KO myocytes by ~8% and led to an attenuation of fractional shortening. These effects were not observed in Ctrl cells. Thus, enhanced Na+ influx modulates electromechanical coupling in cardiomyocytes and delays kinetics of contraction and relaxation with consequences on diastolic properties of the heart. [ABSTRACT FROM AUTHOR]